1. Field of the Invention
The present invention relates to a carbon overcoat for a slider with improved step coverage, and more particularly, to a carbon layer on an air bearing surface of the slider which is redeposited in scratches or trenches to improve spacing loss, corrosion resistance and smoothness.
2. Description of the Related Art
A write head is typically combined with a magnetoresistive (MR) read head to form a merged MR head, certain elements of which are exposed at an air bearing surface (ABS). The write head comprises first and second pole pieces connected at a back gap which is recessed from the ABS. The first and second pole pieces have first and second pole tips, respectively, which terminate at the ABS. An insulation stack, which comprises a plurality of insulation layers, is sandwiched between the first and second pole pieces and a coil layer is embedded in the insulation stack. A processing circuit is connected to the coil layer for conducting write current through the coil layer which, in turn, induces write fields in the first and second pole pieces. A non-magnetic gap layer is sandwiched between the first and second pole tips so that write fields of the first and second pole tips at the ABS fringe across the gap layer.
In a magnetic disk drive a magnetic disk is rotated adjacent to and a short distance (fly height) from the ABS so that the write fields magnetize the disk along circular tracks. The written circular tracks then contain magnetized segments with fields detectable by a read head. An MR read head includes an MR sensor sandwiched between first and second non-magnetic gap layers and located at the ABS. The first and second gap layers and the MR sensor are sandwiched between first and second shield layers. In a merged MR head the second shield layer and the first pole piece are a common layer. The MR sensor detects magnetic fields from the circular tracks of the rotating disk by a change in resistance which corresponds to the strength of the fields. A sense current conducted through the MR sensor results in voltage changes received by the processing circuitry as readback signals.
Hereinafter, for reasons apparent to the skilled artisan, the first and second pole tips, the gap layer, and the MR sensor of a merged MR head, are referred to as "sensitive elements".
One or more merged MR heads may be employed in a magnetic disk drive for reading and writing information on circular tracks of a rotating disk. A merged MR head is mounted on a slider carried on a suspension. The suspension is mounted to an actuator which rotates the magnetic head to locations corresponding to desired tracks. As the disk rotates an air cushion is generated between the rotating disk and an air bearing surface (ABS) of the slider. A force of the air cushion against the air bearing surface is opposed by an opposite loading force of the suspension, causing the magnetic head to be suspended a slight distance (flying height) from the surface of the disk. Flying heights are typically on the order of about 0.05 .mu.m.
A magnetic head has a magnetic height corresponding to the distance between the center of a magnetizable layer on a magnetic disk and surfaces of the afore-mentioned sensitive elements facing the magnetic disk. This spacing is the aggregation of one-half the thickness of the magnetizable layer, the thicknes overcoat on the magnetizable layer, the flying height, the thickness of any overcoat on the slider and on the sensitive elements, and, sometimes a recession of the sensitive elements from a nominal plane of the slider. The sum of these thicknesses and heights determines the spacing loss of a magnetic head because it reduces the bit density achievable by the head. In this regard, bit density is the number of bits written by a head per square inch of a magnetic disk. When the sensitive elements of the magnetic head are positioned closer to the disk, bit density increases because bits are written closer together along a track and more tracks are written per width of the disk.
The slider and the sensitive elements of a magnetic head are subjected to wear during take off and landing of the slider with respect to the magnetic disk. When the sensitive elements are worn, their dimensions change and reduce the quality of head performance. Accordingly, an art has developed to provide an overcoat for the slider and sensitive elements of a magnetic head; this overcoat is sometimes referred to as a wear layer. There is a strong felt need to keep the overcoat as thin as possible in order to minimize its contribution to spacing loss.
During construction, the ABS of a slider and the sensitive elements of a magnetic head are lapped by a grinding or polishing process. The material of the slider may be AlTiC which is typically 70% Al.sub.2 O.sub.3 and 30% TiC. The material of the sensitive elements is typically NiFe. Lapping causes scratches or trenches in a slider's ABS and in the sensitive elements of a magnetic head. The trenches have side walls and are bounded by peaks and valleys. A typical peak-to-valley dimension can be 10 nm after lapping.
A typical overcoat may include a 1 nm adhesion layer of Si under a 9 nm carbon layer. These layers are usually formed on the ABS of the slider and the sensitive elements by sputter deposition. Since sputter deposition is very directional, the layers do not cover vertical (perpendicular to ABS) or near vertical side walls of walls of the trenches. The layers cover the peaks and flat surfaces and, to a lesser extent, sloping surfaces. Uncovered side walls are potentially exposed and can corrode. Further, material deposited on the peaks and flat surfaces increases the thickness of the overcoat layer and, with it, the spacing loss.